The lung is constantly bombarded by inhaled particles and antigens, and has evolved numerous defense mechanisms that guard against the development of inflammation due to otherwise innocuous substances. These defense mechanisms include mucociliary clearance, the mucosal immune system, and epithelial apical junctional complexes (AJC). In recent years there have been significant advances in our understanding of junctional complex structure and function. However, most research to-date has been conducted with model epithelia and in non-pulmonary tissues, and many questions remain about the function of epithelial junctional complexes at mucosal surfaces. The relationship between barrier structure, antigen sampling by intraepithelial dendritic cells (DC), and sensing of mucosal danger needs further study. Interestingly, airway epithelial junction dysfunction is increasingly associated with asthma, but the underlying mechanisms involved and consequences for airway inflammation remain poorly understood. Furthermore, there are no good assays of outside/in airway permeability in clinical use. Here we show that Th2 cytokines, synthetic double stranded RNA (dsRNA), and respiratory syncytial virus (RSV) induce striking disassembly of airway AJC. We identified a novel signaling pathway linking dsRNA and RSV with protein kinase D (PKD) and cytoskeletal remodeling resulting in airway epithelial junction dysfunction. Very little is known about the expression and function of PKD in the lung, but emerging evidence suggests that this versatile signaling molecule may play an important role in mucosal immunity in general. We next used a mouse model of mucosal sensitization with endotoxin-free ovalbumin (Ova), which when inhaled together with the dsRNA polyI:C, results in allergic-type inflammation two weeks later following challenge with Ova alone. Using reciprocal bone marrow chimeric mice, toll-like receptor 3(TLR3) expression was required in radioresistant (stromal) cells in order for dsRNA to act as a pro-allergic inhaled adjuvant. Here we will build on these data and propose a translational research program that will provide new insights into airway epithelial barrier function and epithelial:DC cross-talk of relevance to respiratory viral infections and allergic airway inflammation. We propose four specific aims that will: (1) Define the precise roles of epithelial PKD and dsRNA sensors during mucosal sensitization, (2) Test the hypothesis occludin overexpression inhibits mucosal allergen sensitization, (3) Test the hypothesis that RSV infection causes sustained dysfunction of the airway epithelial barrier in a PKD-dependent manner, and (4) Develop the Leaky Lung Test, a clinically useful and non-invasive assay of outside/in airway permeability.